Re: How fast is the nec v20 compared to a 286?

Posted on 2016-08-27, 17:39

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by Scali

in Milliways

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Last time I tried it pcem was 20% or so faster than it should be for xt, as a result one can get a more accurate result with dosbox because of its finer grain cycle setting where pcem only gives you presets. Depends on what you mean by 'accurate'... DOSBox allows you to accurately tune the speed, …

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Re: IBM PC hardware clock division (XT 14MHz clock)?

Posted on 2016-08-27, 17:36

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by Scali

in PC Emulation

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Not everything is based on the 14318180 Hz clock. Yes, to elaborate on that... CGA cards *are* based on the 14138180 clock. In fact, that's the reason why that clock is used: it's the standard NTSC frequency. You want the CGA card (CRTC and other logic) to work at this clock as well, synced with …

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Re: Sound Blaster Pro bug

Posted on 2016-08-27, 17:07

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The thing is, I can't quite understand why the samples sounds halved. For example, when playing 44kHz mono or 22kHz stereo, DSP is configured to play 44kHz samples per second in either case. I think that is why: If you set the DSP to 44 KHz, it is 44 KHz in mono, but 22 KHz in stereo, so that's why …

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Re: IBM PC hardware clock division (XT 14MHz clock)?

Posted on 2016-08-27, 15:32

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by Scali

in PC Emulation

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So the DMA controller takes 1 cycle for each byte to transfer, so about 4.77 MegaBytes(MB) per second, not depending on CPU speed? No, each byte takes 4 cycles to transfer on a PC/XT at 4.77 MHz. Also, of course DMA and CPU have to share the bus, so when DMA transfers a byte over the bus, the CPU …

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Re: IBM PC hardware clock division (XT 14MHz clock)?

Posted on 2016-08-27, 14:39

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by Scali

in PC Emulation

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- DMA by about 9 on average to get it's transfer rate in bytes/second? The DMA controller runs at 4.77 MHz, so same as a stock PC/XT CPU. DMA controller speed is fixed, like the PIT speed, so they don't vary with CPU speed on later systems. They're always 4.77 MHz and 1.19 MHz respectively. - Adlib …

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Re: The year is 1990 and you still have a PC/XT and can't upgrade. Which games are you playing?

Posted on 2016-08-27, 14:21

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by Scali

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To elaborate, it was a Commodore PC10-III, which we got in 1988 I believe. It came with a Paradise PVC4 onboard video chip, which was capable of both CGA/Plantronics and MDA/Hercules. Initially we got it with a 12" Hercules screen. Later got a Philips CM8833 to use CGA colour.

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Re: Sound Blaster Pro bug

Posted on 2016-08-27, 13:44

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

How is that a bug in the SB Pro though? I mean, it sounds like the game just doesn't bother to take the SB Pro out of stereo mode after you exit it. Since some games are written only for regular Sound Blaster, they don't even know about mono or stereo mode, so they never bother to reset it (they …

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Re: How fast is the nec v20 compared to a 286?

Posted on 2016-08-27, 13:38

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by Scali

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old benchmarks shows dosbox set at x cycles equal to pc/xt speed, run old 8088 games and they play at a reasonable speed. topbench show dosbox set at y cycles equal to pc/xt speed, run old 8088 games and their speed is off. Well, DOSBox' speed is off, that's the problem. In DOSBox, instructions …

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Re: YMF71x vs ES1688 Comparison Thread

Posted on 2016-08-27, 11:26

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

James-F wrote: I have found a bug plaguing all the SB-Pro cards, but it deserves it's own thread. Hum, but the SB-Pro is the de-facto standard OPL3 card... so aren't all other cards buggy when they don't do what the SB Pro does? 😀

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Re: How fast is the nec v20 compared to a 286?

Posted on 2016-08-27, 07:43

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by Scali

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The old benchmarks match up speed better in dosbox than topbench. How is DOSBox any kind of indication of speed? It doesn't even try to make different instructions take different amounts of time. All instructions are 'one cycle'. Which is completely unrepresentative of how a real CPU works. Try …

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Re: How fast is the nec v20 compared to a 286?

Posted on 2016-08-26, 20:02

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by Scali

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awgamer wrote: Last I tried topbench the results didn't line up with results from all the other benches I've run. As you can read on the topbench site, most early benchmarks are severely flawed.

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Re: How fast is the nec v20 compared to a 286?

Posted on 2016-08-26, 17:54

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by Scali

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And The Oldskool PC Benchmark: https://dosbenchmark.wordpress.com/

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Re: PCI-E soundcards with FM chip?

Posted on 2016-08-26, 16:01

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Like I said, the necessity for VGA to remain compatible is the reason that it HAS remained compatible. My point is that it *has* remained compatible. So apparently it is technically possible to retain compatibility despite the ever-changing buses and chipsets. I said "it is up to the people that …

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Re: PCI-E soundcards with FM chip?

Posted on 2016-08-26, 13:30

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Also, my comment about VGA is obviously directed at the fact that VGA devices generally work together and the interface itself is still common. I don't know anything about VGA being emulated, and this isn't really the place for a discussion on that subject. I think it is relevant, since video cards …

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Re: How to enable Matrox OpenGl with Parhelia and V2

Posted on 2016-08-26, 13:01

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Properly written OpenGL code on Windows will go via the ICD interface: 'Installable Client Driver'. This means the application can get a list of all installed OpenGL drivers, and pick the one they one (or let the user pick). You can see this list with GPU Caps Viewer for example: http://www.ozone3d. …

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Re: PCI-E soundcards with FM chip?

Posted on 2016-08-26, 12:18

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Computers are weird. Especially when we're talking about compatibility with 25 year old standards that have been mostly replaced since Windows 98 and DirectSound. Compatibility is the only redeeming value of the PC platform. VGA hasn't changed much Are you kidding me? Modern GPUs have absolutely …

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Re: PCI-E soundcards with FM chip?

Posted on 2016-08-26, 07:47

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The difference I think is that VGA compatibility has been standard for decades, where as SB DOS compatibility on motherboards died off several years ago as far as I know. If anything you'd have to have a motherboard that allowed a PCI-E card to have direct access to all of the resources required …

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Re: CGA composite output via VGA + composite converter

Posted on 2016-08-25, 16:07

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by Scali

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

No. The colours on CGA composite are a direct result of the high frequency pixel data and the colorburst. VGA uses a different frequency, so its scanlines are not directly compatible with NTSC. VGA to composite converters capture a frame and regenerate a new signal at NTSC frequency (dropping frames …

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Re: How fast is the nec v20 compared to a 286?

Posted on 2016-08-25, 14:50

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by Scali

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but IBM created a mutant called PC/XT 286. ^_^ The irony is that the PC/XT 286 uses zero-waitstate memory, where the PC/AT uses a waitstate on memory. This makes the PC/XT 286 considerably faster at the same clockspeed (which again goes back to my point of 'there's no such thing as 286 performance' …

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Re: How fast is the nec v20 compared to a 286?

Posted on 2016-08-25, 14:31

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by Scali

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BloodyCactus wrote: wouldnt the biggest impact on all these cpu be external ram speed and wait states That, and the type of code you run. Eg, 8088 is slow at EA... V20 is fast at EA. If you optimize your code for 8088, you avoid slow EA. Therefore, code optimized for 8088 won't gain much on V20.

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